The present invention relates to a driving system for an electrochromic display device which includes an electrochromic material held in electrode carrying support plates to manifest reversible variations in the light absorption properties in response to current applied thereto.
Using memory function of an electrochromic display device, several kinds of driving circuits were proposed so as to maintain the degree of coloration of selected ones of the segmented display electrodes uniform, one of which was disclosed in a copending U.S. patent application Ser. No. 893,513 filed Apr. 4, 1978 by Hiroshi Hamada et al., assigned to the present assignee, now U.S. Pat. No. 4,210,907.
An abstract of U.S. Pat. No. 4,210,970 is as follows
A driving system was provided for an electrochromic display device in which the coloration state is maintained for several hours through several days after the removal of the coloration voltage as long as the electrochromic device is held in an electrically open state. The electrochromic display device included a predetermined number of display segments, each of the combinations of the display segments defining a different one of the desired display patterns. The display segments placed in the coloration state were electrically connected to each other during the memory period in order to uniform the coloration degree of each of the selected display segments. In a preferred form, a detection means was provided for detecting the potential of the selected display segments, which are held in the memory coloration state. The write-in, or, coloration operation was again conducted when the potential of the selected display segments became higher than a preselected level.
However, the conventional driving circuits as disclosed in Ser. No. 893,513 still had defaults as follows: (1) since pulse-like signals were needed to be generated for coloration and bleaching purposes in the driving circuit of Ser. No. 893,513, a driving circuit required for this purpose was limited in which case a simple driving circuit to be used for driving a light emitting diode was not available; (2) a control circuit became complex; and (3) a predetermined degree of coloration of the segmented display electrodes was prevented by leak current inevitably occuring in the coloration stages.
Therefore, it is important and necessary to effectively maintain uniform the degree of coloration of selected ones of the segmented display electrodes by means of a simplified control circuit.